EP0966049B1 - Piezo-electric motor with integrated position sensor - Google Patents

Description

The present invention relates to a rotary piezoelectric motor provided with means for providing information on the position of its rotor relative to that of its stator. It also relates to a rotary actuator provided with such a piezoelectric motor with integrated position sensor.

In fact, the idea underlying the invention is based on the technical features of the piezoelectric motors, to which one or more elements are adapted to calculate the position of the rotor relative to that of the stator. It leads in practice to a thorough integration, because the said element or elements operate according to the very principle of the motors, that is to say using piezoelectric ceramic components, but in the opposite direction. In some applications, the invention could be considered as a motorized position sensor.

The principle of the motor is to transform a signal of an electrical nature into a mechanical deformation, while that which is the basis of the invention allows the return of an electrical signal reflecting the vibratory state of the engine, which contains several information that can be used for example in a rotary actuator.

• la possibilité d'utilisation sous une température de fonctionnement sévère (de l'ordre de -40° C à +140° C),
• une très bonne linéarité (de l'ordre de ±0,1% ou inférieure),
• une très bonne répétabilité (de l'ordre de 0,1% ou inférieure),
• une résolution angulaire fine (de l'ordre de 0,1°),
• une vitesse de rotation importante (de l'ordre de 1800°/s),
• une durée de vie importante (de l'ordre de 3 x 10⁶ cycles, avec un cycle étant égal à un aller-retour sur 90° d'angle).

A piezoelectric motor incorporating a position sensor based on the same principle also has characteristics giving it qualities particularly suitable for operation in a rotary actuator used in harsh environments, for example in the automotive field for the automotive industry. control of the movement of an air intake flap to adjust the power of the engine of the vehicle. The criteria required for the position sensor include:

• the possibility of use under a severe operating temperature (of the order of -40 ° C to + 140 ° C),
• very good linearity (of the order of ± 0.1% or less),
• a very good repeatability (of the order of 0.1% or less),
• a fine angular resolution (of the order of 0.1 °),
• a high rotation speed (of the order of 1800 ° / s),
• a long life (of the order of 3 x 10 ⁶ cycles, with a cycle being equal to a round-trip over 90 ° angle).

In this particular application, a central control unit makes it possible to control the position of the air intake flap in order to regulate the power of the engine. The position of the shutter must be precise in order to take into account all the parameters that govern the optimization of the cylinder feed according to the driving conditions of an automobile. The role of the actuator is then to receive the commands from the control unit, and to position the shutter according to orders in accordance with the specifications of the function (speed, precision, high torque, despite a small device and low weight).

The required operating parameters are therefore of a very high level.

A typical configuration, for the same kind of application, could be based on a DC motor, provided with the case of a gear reduction gear. The positioning accuracy required of course implies the existence of a position sensor returning a signal to achieve a conventional position control. Traditional copying potentiometers, however, are not efficient enough, particularly in terms of temperature, rotation speed and lifetime to be used.

Magnetostrictive sensors would better meet the specifications, but they are expensive and bulky.

Alternatively, the actuators can use torque motors that work, as for DC motors, with a resistive torque achieved by a return spring. The current regulates a position of the spring but it is still necessary to add a position sensor giving an electrical signal (type feedback potentiometer or magnetic sensor with or without contact) performing a closed loop control.

Finally, there are configurations with stepper motors, but they also ensure the safety of positioning by means of a position sensor performing said closed loop. The stepper motor receives from the control unit the number of pulses needed to move the desired number of steps to reach its position. It theoretically does not need a position sensor. However, this only works if the initial position of the actuator is known.

Systems using stepper motor actuators are therefore obliged to perform a zeroing phase as soon as they are powered up. During this phase, the control unit rotates the actuator for a time slightly longer than the time required to go from one stop to the other, and in a given direction. After this phase, the control unit knows exactly where the actuator and the corresponding air intake flap are, and normal operation can begin. The disadvantages of this method are clear: the time spent by the actuator to lose the steps while it is already in abutment is lost, and the air intake only starts to work with delay. In addition, the actuator, vibrating when it comes into abutment, makes noise.

Furthermore, the possible blockage of the air intake flap for example due to frost, frost or any other mechanical blockage is ignored by the control unit, which continues to send his orders while the position initial was lost. There is then malfunction of the electrical adjustment of the air intake. This is why we must also add a position sensor, allowing still work in closed loop.

One of the objectives of the invention is to eliminate the aforementioned drawbacks, in particular by making it possible to detect the angular position or possibly the blocking of the actuator, as well as any loss of position due to a loss of synchronization between the orders received and movement. It also stops the engine quickly if necessary.

Another object of the invention is to achieve this without increasing the complexity of the system, and therefore remaining in a reasonable economic environment.

• rapide,
• précis,
• doté d'un couple élevé, notamment à basse vitesse,
• peu volumineux,
• de faible poids,
• silencieux,
• fonctionnel sans réducteur,
• dépourvu de problèmes de compatibilité électromagnétique ; et
• doté d'une fonction de diagnostic.

In addition to the criteria presented above, the actuator based on a piezoelectric motor according to the invention is designed to perform particularly advantageously any function within a very demanding environment, because it is:

• fast,
• specific,
• with high torque, especially at low speeds,
• not bulky,
• low weight,
• quiet,
• functional without reducer,
• without problems of electromagnetic compatibility; and
• equipped with a diagnostic function.

Compared to its predecessors of the prior art, the invention also carries out this last essential function leading to a possibility of diagnosis: it transmits to the control electronic central unit, a message indicating either the loss of position, the blocking.

This diagnostic function is interesting for two reasons: firstly during the manufacture, for example of said electrical adjustment system of the air intake, since it allows to quickly check the correct operation, and other hand during normal operation, since any blockage is identified by the central control unit, which can then adopt appropriate backup strategies.

• générer un signal sinusoïdal par un dispositif intégré dans le rotor ;
• comparer la phase dudit signal avec un signal sinusoïdal de référence reflétant l'état vibratoire du stator ;
• calculer la position relative ou absolue de l'un par rapport à l'autre sur une longueur d'onde commune aux signaux sinusoïdaux ;
• détecter des pertes de positionnement ou de blocages de l'un par rapport à l'autre.

In general, the invention therefore relates to a method for electronically calculating the angular position of a rotor with respect to a stator equipped with at least one piezoelectric ceramic layer powered by sinusoidal signals, said rotor and stator belonging to a rotary piezoelectric motor, characterized in that it is based on the respective vibratory states of the rotor and the stator, and in that it comprises the following steps:

• generating a sinusoidal signal by a device integrated in the rotor;
• comparing the phase of said signal with a reference sinusoidal signal reflecting the vibratory state of the stator;
• calculate the relative or absolute position of one with respect to the other over a wavelength common to the sinusoidal signals;
• detect positioning losses or blockages of one relative to the other.

The invention also relates to a rotary piezoelectric motor implementing the above method.

More specifically, said device integrated in the rotor is a piezoelectric sensor undergoing the deformation transmitted by the sinusoidally excited stator by the piezoelectric ceramics of the motor, and emitting a sinusoidal signal out of phase with a stator reference signal.

Thus, the engine's own technical potentialities are used to include a sensor, which amounts to optimizing the dual engine / sensor configuration, in particular by preserving its compactness without there being a corollary increase in the manufacturing cost.

This is in no way a system of reading the position reported on the engine, as is the case in almost all other configurations, but a device inherent in the engine, which uses very simply the reversibility of the technical phenomenon on which said engine rests.

Preferably, the rotor piezoelectric sensor is fixed on the periphery of the rotor.

The rotor sensor thus provides one of the terms of the comparison to be made to know either the angular position of the rotor relative to the stator or the existence of a problem.

According to one possibility, the stator reference signal constituting the other term of the comparison is one of the sinusoidal input voltages applied to piezoelectric ceramics imparting stator deformation.

This solution is in line with the greatest technical simplification and is economically the most favorable.

According to one variant, the second term of the comparison can be provided by the piezoelectric ceramics equipping the stator, which themselves comprise a piezoelectric sensor consisting of an element operating in the opposite direction, that is to say not subject to a sinusoidal electrical signal, but providing a sinusoidal signal in response to distortion printed by the polarized elements.

The location and shape of said sensor depend on the structure of the piezoelectric motor.

If it is a traveling wave motor, the stator piezoelectric sensor is placed between two groups of portins of the ceramic layer subjected to different sinusoidal electrical voltages.

For the record, it is recalled that in these motors, a ring piezoelectric ceramic is alternately positively and negatively polarized on consecutive portions forming groups separated from each other. In n consecutive portions, the ceramic will undergo an inverse deformation at the location of the + and at the place of - when the same voltage is applied (for example a sinusoidal electrical signal) on one side of these n portions (1). other side is at 0 volts). This results in a corresponding deformation of the stator.

The other n portions of the other groups are also subjected to an electrical signal and deform in the same way.

In the particular case where there are two groups of n ceramics, these are shifted in the space of 1/4 mechanical wavelength. The signals a and b are themselves shifted in time by 90 ° electrical and are of the type sin (ωt) and cos (ωt).

This creates two stationary waves shifted in space and time, resulting in a progressive vibratory wave. In practice, the point of contact with the rotor describes a high frequency ellipse N (ω = 2 xnx N) which allows the drive of said rotor, the tangential component of the transmitted vibration causing the rotation while the normal (axial) component shifts the contacting surfaces of the rotor and the stator, thus allowing the transmission of the rotational movement and the transmission of torque.

In fact, the principle of the traveling wave engine consists of generating a progressive bending wave by superposition of two standing waves. The ceramic sectors are positioned at a periodicity of λ / 2 (where λ is the wavelength of the sinusoidal signals).

The frequency is optimized for resonance operation to increase the amplitude of the vibrations and thus increase the power of the motor.

In order to better regulate this frequency of use (above 20 kHz to be in the ultrasound range and therefore suppress the noise) which varies according to several parameters (temperature, start phase, applied load ...), has said portion of stator ceramic restoring an electrical signal between the two groups of n ceramics. This portion of ceramic (statoric sensor) works in the opposite direction of others. Indeed, the rotating vibration deforms the sensor that it forms and there is creation of an electrical signal, whose operation allows in particular the electronic central unit to correct for example the control frequency.

According to a second possible type of motor, the mode-rotating motors, the stator piezoelectric sensor is an annular piezoelectric ceramic layer stacked at one end of the superposition of layers of piezoelectric ceramics subjected to sinusoidal electrical voltages, causing the deformation of the stator.

In these mode-rotating motors, the principle is slightly different, but there is always creation of a rotating ellipse that drives the rotor. The stator bends continuously rotating, and we find the shift of ceramics in space and the shift of electrical signals in time (one of the type cos (ωt) and the other of the type sin (ωt)), creating a rotating vibration mode.

The spatial configuration is however substantially different, since the ceramics are superposed in groups shifted by 90 ° in space, each ceramic being subjected to a sinusoidal voltage equal to those of the other ceramics of the same spatial group.

In fact, the principle of the mode-rotating motor is to use a vibrating structure in a bending mode whose deformation is rotated.

The position sensor integrated in the piezoelectric motor defined by the invention can operate in multiple applications, and especially, preferably, to constitute a rotary actuator since it is combined with said motor which at the same time becomes the main body of the actuator.

This actuator can additionally integrate an electrical circuit controlling the piezoelectric motor. This hardly alters its compactness.

Finally, a compact actuator having high level characteristics is obtained.

• la figure 1 est une vue éclatée montrant schématiquement les composants fixés au stator dans un moteur à onde progressive ;
• la figure 2 représente un schéma illustratif de fonctionnement pour ce moteur ;
• la figure 3 est une vue en trois dimensions d'un stator déformé ;
• la figure 4 donne l'emplacement du capteur statorique dans un moteur à onde progressive ;
• la figure 5 représente une configuration schématique possible de moteur à rotation de mode ;
• les figures 6a et 6b précisent la représentation de la figure 5 ; et
• la figure 7 est une coupe d'un actionneur basé sur un moteur piézo-électrique à onde progressive.

The invention will now be described in more detail, with reference to the figures, for which:

• the figure 1 is an exploded view schematically showing the components attached to the stator in a traveling wave motor;
• the figure 2 represents an illustrative diagram of operation for this engine;
• the figure 3 is a three-dimensional view of a deformed stator;
• the figure 4 gives the location of the stator sensor in a traveling wave motor;
• the figure 5 represents a possible schematic configuration of a mode-rotating motor;
• the Figures 6a and 6b specify the representation of the figure 5 ; and
• the figure 7 is a section of an actuator based on a progressive wave piezoelectric motor.

The exploded view of the figure 1 shows the piezoelectric ceramic stage (1) surrounded by two rings (2, 3) by which the sinusoidal electrical signals are applied to obtain a mobile deformation to be transmitted to the stator (4) itself.

In this configuration, the (+) and (-) portions form two groups (A, B) separated by zones facing each other, whose respective lengths total a wavelength, and allow a shift of one quarter of mechanical period of said portions.

The figure 2 Explains the electrical operation of this piezoelectric wave motor configuration.

The rotor (5) appears above the stator (4), pressed against it, the arrow (F) materializing the direction of its movement. The two groups (A, B) are represented in a simplified manner, each having two portions of polarity opposite, to which electrical quadrature signals Ccos (ωt) and Csin (ωt) are applied.

The ellipses constituting the displacement of the contact points also appear in this figure, as well as the movement of the wave, symbolized by the arrow (F '), which moves in the opposite direction to the direction of movement of the rotor (5).

The figure 3 gives an idea of the deformation that propagates in the stator (4), seen in instantaneous.

The figure 4 more clearly illustrates the breakdown of the groups mentioned in the description of the figure 1 , and is in fact a top view of the piezoelectric ceramic shown there.

The positively or negatively polarized portions or electrodes alternate in the two groups A and B and are separated by two intervals (C, D) of unequal size as previously defined. The largest separation zone (D) comprises the stator piezoelectric sensor (E).

The Figures 5, 6a and 6b a mode-rotating piezoelectric motor which has a rotational symmetry such as figure 5 only half of the configuration has been shown. The rotor (5) is always in contact with the stator (4), but the structure changes at the level of the piezoelectric ceramics: these are arranged in the form of superposed rings (1, 1 ', 1 ", 1"' ) under the stator (4), under which they are prestressed by compression.

The global polarization scheme appears in figure 6a , while the individual configuration is schematized in figure 6b .

In the lower part of the stack, the statoric piezoelectric sensor (E) obeys the same geometry as the previous levels.

In both cases, as mentioned before, the basis of the invention is to integrate the sensor inside the engine, then to use the information contained in the vibratory state of the stator and the rotor. The angular position of the rotor is determined relative to a reference on the stator. The angle thus defined is proportional to the phase shift between the reference signal and the signal from the sensor located in the rotor. The stator reference signal is provided either by the or a ceramic layer of the stator, as shown previously, either by the signal (U1, U2) of one of the two electrical power supply channels of the motor which is transmitted to the stator.

In the case of a traveling wave motor, the progressive elastic wave at a point of the stator has the expression Uz1 = A1 cos (ωt-nθ1). At a point on the rotor, if the latter passively follows the elastic wave generated in the stator, the expression of the elastic wave will be: Uz2 = A2 cos (ωt - nθ2). Since the position of the rotor is proportional to Δφ, it is sufficient to measure the phase difference between the two signals.

The phase difference Δφ = n (θ1 - θ2) is zero modulo 2π / n, if the motor operates on the mode n, that is to say with the equivalent of n wavelengths distributed on the circumference, and thus has n passages at the zero value of Δφ.

The mode rotation motor has the advantage of having only one wavelength on its periphery. Counting the passages to 0 is simplified, and in fact corresponds to the number of turns.

The information given by the integrated position sensor may be relative in nature (incremental sensor) or absolute.

Indeed, the angle is defined by the phase shift between the stator reference signal and a signal from the rotor sensor. In the first case, the position of a previously measured position is deduced: the displacement is actually measured from the moment when a stator signal is emitted. In the case of the traveling wave motor, for example at five wavelengths on one revolution (five modes) or seven wavelengths on one revolution (seven modes), it is obviously necessary to take into account the transitions of one mode. to the other because the phase difference is canceled when switching from one mode to another. It is therefore not possible to recognize two positions spaced 51.4 ° apart for a seven-mode progressive wave motor, since this corresponds to the same phase difference.

• par exemple pour un moteur à onde progressive à sept modes, le capteur peut donner une position absolue sur 51,4° ;
• pour un moteur à rotation de mode, pour lequel il n'y a qu'un seul mode sur un tour, le capteur peut donner une position absolue sur un tour complet (360°).

In the second case (absolute reading), knowledge of the absolute position can also be detected only over a wavelength. Indeed, a single angle corresponds to a phase shift value, and the position on a mode is defined at mounting:

• for example for a seven-mode progressive wave motor, the sensor can give an absolute position on 51.4 °;
• for a mode-rotating motor, for which there is only one mode on a lathe, the sensor can give an absolute position over a full revolution (360 °).

The absolute position can be obtained in a mode (ie a revolution in the case of a mode-rotating motor) as soon as the current passes, even without rotor movement: the stator reference signal is indeed available (vibratory signal ) before the threshold of movement of the rotor.

However, if necessary, the stator signal can also be obtained after a small movement of the rotor. At 20kHz, the necessary movement is however very weak, and the position is detected almost instantaneously, which corresponds to an almost absolute position sensor signal.

The figure 7 shows a section of an actuator based on a traveling wave motor, the piezoelectric ceramic (1) being of course in contact with the stator (4) which acts on the rotor (5) on which the return force is exerted a spring (6) pressing against the stator (4).

Said figure still shows conventional mechanical elements such as a clamping nut (7) rotor / stator, a connecting piece (8), as well as the elements constituting more specifically the invention: the stator sensor (9) and the sensor rotor (10).

Among the residual advantages of the invention that may be mentioned, which are of a nature to be more clearly understood following the detailed description which has just been made, it may be mentioned that the integration of the sensor allows to eliminate the need for limit sensors in some systems of the type of that of the preferred example. Indeed, the integrated position sensor indicates with sufficient precision the limit switches and thus performs these functions.

This further reduces the complexity and cost of some configurations.

In addition, said integration makes it possible to reduce the wear of the rotor / stator friction layer of the piezoelectric motor when there is a blockage, since it is immediately detected therefrom, and the engine stops or diagnosis of the problem. followed by an attempt to solve it.

Conversely, if the blocking is not detected when the piezoelectric motor is controlled by an electronic system, there is wear at the point or points of contact which then vibrate in static, hence the advantage substantial provided by the diagnostic capability offered by the invention by detecting a frequency variation.

Finally, the integrated sensor makes it possible, if necessary, to suppress a return spring, particularly in the example of adjusting an air intake flap in an automobile. Such a spring, used to facilitate positioning, is indeed no longer necessary because of the intrinsic qualities of the actuator.

The sensor replaces indeed the spring for this function, because it gives in particular a more precise position and especially an electrical signal that allows a closed loop operation of the system.

The above examples are of course not limiting of the invention, which is defined by the following claims.

Claims (9)

1. Method for electronic calculation of the angular position of a mobile rotor (5) with respect to a stator (4) equipped with at least one ceramic piezo-electric layer (1) powered by sinusoidal signals, the said rotor (5) and stator (4) belonging to a rotary piezo-electric motor, characterized in that it is based on the respective vibrational states of the rotor (5) and of the stator (4), and in that it comprises the following steps:

   - generate a sinusoidal signal by a device integrated into the rotor;

   - compare the phase of the said signal with a sinusoidal reference signal reflecting the vibrational state of the stator (4);

   - calculate the relative or absolute position of the one with respect to the other over a wavelength common to the sinusoidal signals;

   - detect positioning or blocking losses of the one with respect to the other.
2. Rotary piezo-electric motor implementing the method according to Claim 1, characterized in that the device integrated into the rotor (5) is a piezo-electric sensor (10) subjected to the deformation transmitted by the stator (4) excited sinusoidally by piezo-electric ceramics (1, 1', 1") of the motor, the sinusoidal signal emitted by the said piezo-electric sensor (10) being out of phase with respect to a stator reference signal.
3. Rotary piezo-electric motor according to the preceding claim, characterized in that the rotor piezo-electric sensor (10) is fixed to the periphery of the motor.
4. Rotary piezo-electric motor according to either of Claims 2 and 3, characterized in that the stator reference signal is one of the sinusoidal input voltages applied to the piezo-electric ceramics (1, 1', 1") communicating a deformation to the stator.
5. Rotary piezo-electric motor according to either one of Claims 2 and 3, characterized in that the piezo-electric ceramics (1, 1', 1") equipping the stator (4) comprise a piezo-electric sensor (9) consisting of an element operating in the reverse direction, in other words not subjected to a sinusoidal electrical signal, but supplying a sinusoidal signal in response to a deformation imposed by the biased elements, which can be the stator reference signal.
6. Travelling-wave piezo-electric motor according to the preceding claim, characterized in that the piezo-electric sensor (E), which supplies the stator reference signal, is placed between two groups (A, B) of biased portions of ceramics subjected to different sinusoidal electrical voltages.
7. Rotating-mode motor according to Claim 5, characterized in that the stator piezo-electric sensor (E), which supplies the stator reference signal, is a stacked cylindrical piezo-electric ceramic layer at one end of the superposition of piezo-electric ceramic layers (1, 1', 1") subjected to sinusoidal electrical voltages causing the deformation of the stator (4).
8. Rotary actuator characterized in that it is based on a piezo-electric motor integrating an angular position sensor according to any one of Claims 2 to 7.
9. Rotary actuator according to the preceding claim, characterized in that it comprises an integrated electronic circuit provided for controlling the piezo-electric motor.

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